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   <title>Zoltan User's Guide:  Nested Dissection by Scotch</title>
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<div align=right><b><i><a href="ug.html">Zoltan User's Guide</a>&nbsp;
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<h2>
<a NAME="PT-Scotch"></a>Nested Dissection by Scotch</h2> Nested
Dissection is a popular method to compute fill-reducing orderings for
graphs and sparse matrices. It can also be used for other ordering
purposes.  The algorithm recursively finds a separator (bisector) in a
graph, orders the nodes in the two subsets first, and nodes in the
separator last.
<p>
Scotch is a library for ordering and partitioning, developed at LaBRI
in Bordeaux, France. PT-Scotch is the parallel module in Scotch. (We
use the names Scotch and PT-Scotch interchangeably.) Scotch is a
third-party library in Zoltan and should be obtained separately from
the <a href="https://www.labri.fr/perso/pelegrin/scotch/">Scotch web
site</a>. Zoltan supports version 5.1 of Scotch.
<p>
If the parameter <a href="ug_order.html#ORDER_METHOD">ORDER_METHOD</a> is
set to SCOTCH, the sequential version of Scotch is called.
If the parameter <a href="ug_order.html#ORDER_METHOD">ORDER_METHOD</a> is
set to PTSCOTCH, the parallel version of Scotch (PT-Scotch) is called.
</p>


<table WIDTH="100%" NOSAVE >
<tr>
<td VALIGN=TOP><b>Order_Method String:</b></td>

<td><b>PTSCOTCH or SCOTCH</b></td>
</tr>

<tr>
<td><b>Parameters:</b></td>

<td></td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp; SCOTCH_METHOD</td>
<td>For now, always set to NODEND</td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp; SCOTCH_STRAT</td>
<td>The Scotch strategy string; see the Scotch documentation.</td>
</tr>

<tr>
<td VALIGN=TOP>&nbsp;&nbsp; SCOTCH_STRAT_FILE</td>
<td>A file that contains an arbitrary long Scotch strategy string; see the Scotch documentation.</td>
</tr>

<tr>
<td VALIGN=TOP><b>Required Query Functions:</b></td>

<td></td>
</tr>

<tr>
<td></td>

<td><b><a href="ug_query_lb.html#ZOLTAN_NUM_OBJ_FN">ZOLTAN_NUM_OBJ_FN</a></b></td>
</tr>

<tr>
<td></td>

<td><b><a href="ug_query_lb.html#ZOLTAN_OBJ_LIST_FN">ZOLTAN_OBJ_LIST_FN</a></b>
</td>
</tr>

<tr VALIGN=TOP>

<td></td>
<td NOSAVE>
<b><a href="ug_query_lb.html#ZOLTAN_NUM_EDGES_MULTI_FN">ZOLTAN_NUM_EDGES_MULTI_F
N</a></b> or
<b><a href="ug_query_lb.html#ZOLTAN_NUM_EDGES_FN">ZOLTAN_NUM_EDGES_FN</a></b>
<br>
<b><a href="ug_query_lb.html#ZOLTAN_EDGE_LIST_MULTI_FN">ZOLTAN_EDGE_LIST_MULTI_F
N</a></b> or
<b><a href="ug_query_lb.html#ZOLTAN_EDGE_LIST_FN">ZOLTAN_EDGE_LIST_FN</a></b>
</td>

</tr>

</table>

<p>
<hr WIDTH="100%">[<a href="ug.html">Table of Contents</a>&nbsp; | <a href="ug_order_local_hsfc.html">Next:&nbsp;
Local Ordering with HSFC</a> |&nbsp; <a href="ug_order_parmetis.html">Previous:&nbsp; Ordering by ParMetis</a>&nbsp; |&nbsp; <a href="https://www.sandia.gov/general/privacy-security/index.html">Privacy and Security</a>]
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